Tweaks on async ipython

[et2010]

Those commits includes following tweaks:

• support :noweb code reference
• Fixed How to preserve leading whitespace for ob-ipython-results :text/plain? #140
• Rewrite company backend, completion is now more robust.
• Replace org-babel-get-src-block-info whenever possible. That function is too heavy, causing lag to evaluation or completion. The performance is improved a lot upon this change. As I can tell, at least the completion is more responsive.
• Rework results rendering. When :results is set to output, it will use the output as results. If no output is available, it will generate a reasonable fake output from ipython evaluation. When :results is set to value, you can use the :ob-ipython-results header arg to specify the result type you want. Inspired by ob-ipython, I also added a text/org type that can be used to format pandas dataframe as org table (tabulate.py is needed). To use it, you shoud add a ipython startup file:

#!/usr/bin/env python
import IPython
from tabulate import tabulate
from pandas import Index

class OrgFormatter(IPython.core.formatters.BaseFormatter):
    def __call__(self, obj):
        try:
            if isinstance(obj, Index):
                raise Exception('Do not format Index object!')
            return tabulate(obj, headers='keys',
                            tablefmt='orgtbl', showindex='always')
        except:
            return None

ip = get_ipython()
ip.display_formatter.formatters['text/org'] = OrgFormatter()

• And other minor tweaks.

It is worth mentioning that setting org-babel-ipython-debug to t has a significant impact on performance of evaluation of ipython block. So I always turn it off except when I want to debug the async process.

Since I use scimax with spacemacs so you'll notice some indentation change. sorry about that.